Diffusion transfer photographic products and processes are known to the art and details relating thereto can be found in U.S. Pat. Nos. 2,983,606; 3,415,644; 3,415,645; 3,415,646; 3,473,925; 3,482,972; 3,551,406; 3,573,042; 3,573,043; 3,573,044; 3,576,625; 3,576,626, 3,578,540; 3,569,333; 3,579,333; 3,594,164; 3,594,165; 3,597,200; 3,647,437; 3,672,486; 3,672,890; 3,705,184; 3,752,836; 3,857,865, all of which are incorporated here in their entirety. Essentially, diffusion transfer photographic products and processes involve film units having a photosensitive system including at least one silver halide layer, usually integrated with an image-providing material. After photoexposure, the photosensitive system is developed to establish an imagewise distribution of a diffusible image-providing material, at least a portion of which is transferred by diffusion to an image-receiving layer capable of mordanting or otherwise fixing the transferred image-providing material. In some diffusion transfer products, the transfer image is viewed by reflection after separation of the image-receiving element from the photosensitive system. In other products, however, such separation is not required and instead the transfer image-receiving layer is viewed against the reflecting background usually provided by a dispersion of a white reflecting pigment, such as, for example, titanium dioxide. The latter type of film unit is generally referred to in the art as integral negative-positive film units and are described, for example, in the above mentioned U.S. Pat. Nos. 3,415,644 and 3,594,165.
Film units containing contiguous silver halide emulsion layers sensitive to the same spectral region are known to the art as shown by the following representative patents.
U.S. Pat. No. 3,505,068 is directed to a photographic element which contains overlying silver halide emulsions wherein the first emulsion is a regular silver haloiodide emulsion and the second contains grains which have an iodide-free shell and a silver iodide core.
U.S. Pat. No. 3,663,228 is directed to a photographic film unit having a plurality of silver halide emulsion layers divided into sets with each set of a different speed while the layers in each set have the same speed but are responsive to different spectral regions. Color filters may be disposed between the layers.
U.S. Pat. No. 3,695,882, is directed to a photosensitive element comprising a support carrying two emulsions, each containing a non-diffusing color coupler. Each emulsion has a different speed and different silver halide-coupler molar ratio. An intermediate layer between the two emulsions is also disclosed.
U.S. Pat. No. 3,846,135 is directed to a synergistic increase in the sensitivity of two superposed silver halide layers when the lower layer is less sensitive than the upper layer and has a maximum density of at least 1.5 compared to a maximum density of at least 0.9 for the upper layer. The lower layer is about 5 to 15.mu. thick.
U.S. Pat. Nos. 3,960,558 and 4,003,744 disclose diffusion transfer film units which employ split silver halide emulsions having dye image-forming material associated therewith and which, in fact, contain dye image-forming material in one of said contiguous layers.
U.S. Pat. No. 3,188,209 is directed to a diffusion transfer film unit wherein the photosensitive element comprises red, green and blue sensitive silver halide emulsion layers with cyan, magenta and yellow dye developers, respectively, associated with said emulsions, wherein each dye developer is positioned between and contiguous to two emulsion layers of the same spectral sensitivity, e.g., the cyan dye developer is positioned between and contiguous to two red sensitive emulsions.
British Pat. No. 874,046, discloses a diffusion transfer film unit which includes an image-receiving layer, and a dye-developer layer interposed and between two blue sensitive silver halide emulsions. After exposure and application of a processing composition, the film unit is brought into superposition with a second image receiving layer to provide a dye image in each receiving layer.
Copending application Ser. No. 38,533, filed May 14, 1979, and commonly assigned, discloses and claims photographic film units which include a plurality of essential layers including at least one photosensitive silver halide layer comprising silver halide grains of a first mean particle size and a second photosensitive silver halide emulsion layer comprising silver halide grains of a second mean particle size; said first and second silver halide emulsion layers being in contiguous relationship with the first silver halide layer being distal to the exposure surface of the film unit; said first and second silver halide layers being free of dye image-forming material but having associated therewith a material which provides a dye image-forming material which is diffusible as a function of the point-to-point degree of silver halide exposure to actinic radiation. The silver halide layer comprises gelatin and inert particles which are compatible with gelatin, non-swelling in alkali and substantially non-film forming, wherein said inert particles are equal to or less than the silver halide grains in average diameter and wherein the silver halide grains are 2.5 microns or less in average diameter. Preferably, the inert particles are derived from a polymeric latex. The photosensitive elements are employed with a layer adapted to receive image-forming material diffusing thereto and means for applying an aqueous processing composition. The intrinsic speed of the second silver halide emulsion layer is preferably greater than that of the first silver halide emulsion layer.